The present invention relates to low reflection glass articles such as automobile glass windows, construction glass, show windows, displays, solar cell glass base substrates, solar water heater glass panels, optical glass parts and the like.
Coating of glass base substrates with films for low reflection treatment to reduce visible light reflectivity of glass base substrates is widely known. An example of a method of utilizing the light interference effect obtained by lamination of two or more films on a glass sheet to realize low reflectivity is the invention of Japanese Unexamined Patent Publication No. Hei-4-357134, which discloses automobile reflection-reducing glass with a two-layer construction, characterized in that a thin-film layer with a refractive index of n1=1.8-1.9 and a film thickness of 700-900 angstroms is coated on at least one surface of a transparent glass sheet as the first layer from the glass side, and then a thin-film layer with a refractive index of n2=1.4-1.5 and a film thickness of 1100-1300 angstroms is coated on the first thin-film as a second layer, whereby the reflectivity on the thin-film coated layer side is reduced by 4.5-6.5% for visible light on the film side entering at an incident angle of 50° to 70° with respect to the normal to the surface. The invention of Japanese Unexamined Patent Publication No. Hei-4-357135 also proposes glass with a low reflection film composed of three layers.
On the other hand, as a method of forming a single layer film on glass to reduce reflection with the film, such as the invention of Japanese Unexamined Patent Publication No. Sho-63-193101 for example, discloses an anti-reflection film obtained by coating and drying an alcohol solution of Si(OR)4 (where R is an alkyl group) containing SiO2 fine particles onto the surface of glass, to attach SiO2 fine particles and an SiO2 thin-film coating it onto the glass surface.
The invention described in Japanese Unexamined Patent Publication No. Sho-62-17044 discloses an anti-reflection film obtained by mixing a metal alcoholate such as tetraethoxysilane with colloidal silica with a particle size of 5-100 nm in a proportion of 1 mole of the metal alcoholate to 1 mole of the colloidal silica, hydrolyzing a mixed solution obtained by dissolving it in an organic solvent such as alcohol, and coating the partially condensed sol solution onto an optical element surface, and heat treating it.
Also, the invention described in Japanese Unexamined Patent Publication No. Hei-11-292568 discloses visible light low reflection glass obtained by forming a low reflection film with a thickness of only 110-250 nm, containing linear silica fine particles and silica at 5-30 wt % with respect thereto.
It is known, as described in Optical Engineering, Vol.21, No.6, (1982), page 1039-, that such low reflection films which are single-layer low refractive index layers have low incident angle dependence of reflectivity, and that their low wavelength dependence of reflectivity results in a wide wavelength region of low reflection.
The method of coating a glass base substrate with a coating comprising two or more laminated film layers can reliably provide low reflection of visible light, but since the film thickness must be strictly specified to satisfy the interference conditions and the coating must be performed at least twice, the production costs are undesirably increased. Moreover, films of two or more layers have higher incident angle dependence of reflectivity, and therefore the reflectivity is not always lowered outside of the designed incident angle range. In this respect, coating a glass base substrate with a single-layer low reflection film with a low refractive index results in a wider wavelength range of low reflectivity.
With the anti-reflection films disclosed in Japanese Unexamined Patent Publications No. Sho-62-17044 and No. Sho-63-193101, the anti-reflection performance provided is insufficient. Also, the visible light low reflection glass disclosed in Japanese Unexamined Patent Publication No. Hei-11-292568, while being a single-layer low reflection film that realizes low reflectivity and exhibits sufficient film strength in evaluation by surface abrasion such as a back-and-forth abrasion test, is also associated with the problem of inadequate film strength in most stringent abrasion resistance tests such as the Taber abrasion test. In addition, in the case of oil adhesion which cannot be removed by wiping with a dry or wet cloth, the problem of increased reflectivity occurs.
It is an object of the present invention to provide a low reflection film for visible light or infrared light, which exhibits low reflectivity with a single layer, has high film strength as evaluated by anti-abrasion tests, and exhibits excellent contamination resistance.